CVE-2026-52869MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal
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It affects modelcontextprotocol python-sdk and 1 other product. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
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The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to 1.27.2, the SSE and stateful Streamable HTTP transports mcp.server.sse.SseServerTransport and mcp.server.streamable_http_manager.StreamableHTTPSessionManager route requests to existing sessions using only the session_id query parameter or Mcp-Session-Id header without verifying the authenticated principal that created the session, allowing a different bearer-token-authenticated client with a known session ID to inject JSON-RPC messages into that session. This issue is fixed in version 1.27.2.
- CVSS
- 7.1 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L
- Weakness (CWE)
- CWE-639
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- GitHub_M
- NVD analysis
- Analyzed
- Record last updated
- Jul 16, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
modelcontextprotocol python-sdk modelcontextprotocol:python_sdk (from the name) | before 1.27.2 | CNA record |
lfprojects mcp_python_sdk lfprojects:mcp_python_sdk | before 1.27.2 | NVD |
References
- https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58x-refsource-confirm, vendor-advisory
- https://github.com/modelcontextprotocol/python-sdk/pull/2690x-refsource-misc, issue-tracking, patch
- https://github.com/modelcontextprotocol/python-sdk/pull/2719x-refsource-misc, issue-tracking, patch
- https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00x-refsource-misc, patch
- https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0ax-refsource-misc, patch
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2x-refsource-misc, release-notes
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.